tests ~ reorganize tests

tests/by-util/test_stdbuf.rs

@@ -0,0 +1,13 @@
+use crate::common::util::*;
+
+#[test]
+fn test_stdbuf_unbuffered_stdout() {
+    if cfg!(target_os = "linux") {
+        // This is a basic smoke test
+        new_ucmd!()
+            .args(&["-o0", "head"])
+            .pipe_in("The quick brown fox jumps over the lazy dog.")
+            .run()
+            .stdout_is("The quick brown fox jumps over the lazy dog.");
+    }
+}